Newborn horizontal cells migrate bi-directionally across the neuroepithelium during retinal development

Abstract

Cell migration plays an important role during the development of the retina. In this work we have studied the migration of newborn horizontal cells in avian embryonic retina. Using the pattern of the early expressed transcription factors Lim1 and Prox1 we have shown that horizontal cells migrate bi-directionally from their site of birth, close to the ventricular side, to the adjacent (vitreal) side of the neuroepithelium, where they align just next to the prospective ganglion cell layer before migrating back again to their final laminar position in the external part of the inner nuclear layer. The migration occurs between Hamburger and Hamilton stages 24 and 33,which is equivalent to embryonic day 4.5 and 8. Between stages 26 and 30 the horizontal cells reside close to the ganglion cell layer and intra ocular injections of a cytochalasin D, an actin polymerisation blocker that inhibit migration, at stage 29 interfered with the migration of the horizontal cells to their final destination. Furthermore, using biolistic gene transfer with a green fluorescence protein expression vector of retinal slices we were able to record ventricle-directed migration by time-lapse microscopy. Combining biolistics with immunohistochemistry we showed that transfected cells, which have also been translocated in a ventricular direction were positive for the horizontal cell markers Lim1 and Prox1. The alternative path of migration that is described in this work differs from the generally accepted one for horizontal cells and this knowledge will influence the view of how the molecular determination of horizontal cells is specified.

Lim1 Is Essential for the Correct Laminar Positioning of Retinal Horizontal Cells

“…Lim1 is also widely expressed throughout the developing and adult CNS, but the precise roles of Lim1 within neuronal populations remain poorly defined. Interestingly, Lim1 transcripts and protein were localized to differentiating and mature retinal HCs (Liu et al, 2000;Edqvist and Hallbook, 2004). However, because of the headless Lim1Ϫ/Ϫ phenotype (Shawlot and Behringer, 1995), analysis of the function of Lim1 in the retina has not previously been addressed.…”

“…Despite the recent progress in elucidating the factors regulating HC fate specification, virtually nothing is known about factors regulating later aspects of HC development. Postmitotic, differentiating HCs are distributed throughout the neuroepithelium and thus require a localization mechanism(s) to direct appropriate terminal laminar positioning (Hinds and Hinds, 1979;Liu et al, 2000;Edqvist and Hallbook, 2004). Once localized to the correct layer, HCs differentiate in response to their afferent innervation and establish functional connections with synaptic partners (Raven et al, 2007).…”

Development of the lymphatic vascular system: A mystery unravels

“…This reprogramming was associated with repression of several BEC-specific genes such as E-selectin, interleukin-8, laminin, collagens, neuropilin-1, and VEGF-C, and with induction of several lymphatic-specific genes, including VEGFR-3, podoplanin, and desmoplakin I and II (Hong et al, 2002;Petrova et al, 2002). In addition to its function in reprogramming transcriptional profiles, Prox1 might specify cell fates also by promoting the exit of progenitor cells from the cell cycle and by inducing postmitotic differentiation programs, as has been found during the development of the mammalian retina and the eye lens Dyer et al, 2003;Edqvist and Hallbook, 2004). However, because Prox1 does not appear to regulate the cell cycle in differentiating LEC, the mechanisms underlying the Prox1-mediated induction of cellular differentiation likely are cell-type specific Wigle et al, 2002).…”

Cellular expression of midkine‐a and midkine‐b during retinal development and photoreceptor regeneration in zebrafish

“…Prox-1, a homeodomain protein required for horizontal cell development (Dyer et al, 2003) and is expressed in chicks and mammals by horizontal, amacrine and bipolar cells (Dyer et al, 2003;Belecky-Adams et al, 1997;Edqvist and Hallbook, 2004). At 72 hpf, Prox-1 labels the narrow band of horizontal cell bodies at the outer boundary of the INL, though mdka expression in these cells is not detected at this time ( Fig.…”